1. Field of the Invention
This invention relates generally to sealing members of elastomeric material of the type that are used as packings between the annular surfaces of a casing and a reciprocating or rotating shaft.
2. Description of the Prior Art
It is conventional to use a plurality of annular sealing rings of elastomeric material having a generally V-shape in cross section for a packing assembly to form a seal between a shaft and casing in which the shaft is mounted for either reciprocating or rotating movement. Examples of this general type of sealing members and packing assemblies formed thereby are disclosed in U.S. Pat. Nos. 2,665,151; 2,907,596; 2,962,314; 3,013,830; 3,342,500; 3,386,745; 3,447,819; 3,519,280; 3,680,874 and 3,790,179.
As is disclosed in the prior art patents referred to in the preceding paragraph, the sealing members are generally nested together between the end walls of a packing housing. At least on of the end walls of the packing housing is removable, and when installed, can be axially adjusted toward and away from the other end wall so that axial compression can be applied to the nested sealing members. The axial pressure applies forces on the nested sealing members that increase the sealing pressure applied in a radial direction by the sealing members against the surfaces of the shaft and packing housing.
In the unstressed condition of the sealing members, the sealing surfaces are of course spaced apart a distance greater than is the case in the installed condition; the sealing surfaces are moved toward each other in the installed condition in order to apply sealing pressure. For installation purposes, it is of course desirable that the sealing surfaces be easily moved toward each other. Conversely, however, once installed, it is desirable that there be high resistance to movement of the sealing surfaces toward each other so that adequate sealing pressure is applied by the sealing surfaces against the respective surfaces of the shaft and packing housing. Stated another way, it is on the one hand desirable for there to be relatively low resistance to compression of the sealing surfaces toward each other for installation purposes, but on the other hand, it is desirable for there to be high resistance to compression of the sealing surfaces toward each other after the sealing members are installed.
Some prior art sealing members, for example, the sealing members disclosed in the above referred to U.S. Pat. Nos. 2,665,151 and 3,013,830, simply provide for the sealing surfaces to be spaced apart a substantially greater distance in the unstressed condition of the sealing member with respect to the installed condition of the sealing member. This requires that the sealing surfaces be compressed toward each other from the unstressed condition to the spacing required for the installed condition, in which installed condition, substantial pressure is exerted by the sealing surfaces tending to spread the sealing surfaces. This, of course, increases the difficulty of installing the sealing members. Another approach in the prior art, as shown for example in U.S. Pat. Nos. 3,169,776; 3,342,500 and 3,680,874, is to insert a second element such as an O-ring or garter-type spring between the legs of the V-shaped sealing member to increase the stiffness.